Printing apparatus

ABSTRACT

A printing apparatus for printing onto objects is disclosed. The apparatus comprises a plurality of carrying devices ( 104 ) for carrying objects ( 108 ) to be printed on, the carrying devices ( 104 ) each comprising a rotatable handling device configured to hold and rotate an object. A track ( 102 ) defines a path along which each of the plurality of carrying devices can be moved. A plurality of processing stations ( 106 A- 106 F) are arranged along the track and comprising at least one printing station ( 106 C). A controller ( 110 ) is configured to independently control the position and speed of each of the carrying devices ( 104 ) with respect to the track. The handling device is arranged to rotate an object at at least one of the plurality of processing stations by coupling to a driving device ( 610 ) disposed at the at least one processing station such that torque is transmitted from the driving device to the handling device.

The present disclosure relates to a printing apparatus in which objectsare carried between processing stations including at least one printingstation for printing an image onto the surface of an object.

BACKGROUND TO THE INVENTION

Many industries require high volume complex printing processes in whicha large number of objects are processed in a succession of treatments.For example, each object in such a process might receive several inkdepositions and finishing treatments. One example of such an industrialprinting process is digital can printing, in which high resolutiondigital images are applied to the bodies of cylindrical cans in asequence of printing operations.

A known problem in the field of high volume complex printing processesis how to arrange processing stations and carrying devices for theobjects in such a way as to maximize the rate at which objects areprinted (throughput) while minimizing the physical space required forthe apparatus.

In order to process a large number of objects efficiently, industrialprinting processes typically involve performing different operations ona number of objects simultaneously. The objects are carried through asuccession of processing stations in a staggered progression, with eachobject undergoing a different process to the other objects at any onetime. Processes typically include the loading and unloading of objects,inspection, the application of one or more ink depositions, drying andthe application of an over print varnish.

A known apparatus for carrying objects between printing stations is amandrel wheel system (also known as a spindle disc). In mandrel wheelsystems, a plurality of mandrels are fixed at an equal spacing around arotating or indexing wheel. The wheel indexes through a sequence ofincremental rotations, during which objects are carried by mandrels fromstation to station. In each incremental rotation of the wheel, eachmandrel is moved into the position previously occupied by a neighbouringmandrel. At any one time, an object at a given mandrel wheel isundergoing a process that was performed on an object at the neighbouringmandrel wheel during the previous step.

A problem with mandrel wheel systems is that the duration of eachindexing step is limited by the slowest process in the sequence. Objectsthat are undergoing a relatively quick process must therefore be heldinactive for some time while the slowest process is being completed. If,for example, the slowest process takes twice as long as a fasterprocess, objects will be required to remain inactive at the fasterprocessing station for twice the duration that the process takes toperform. This inactive time is a source of inefficiency in the printingprocess.

Mandrel wheel systems are also limited by the requirement that theminimum distance between neighbouring mandrels be at least as large asthe length of the longest processing station. Hence the overallcircumferential length is at least the length of the longest processingstation multiplied by the number of processing stations. Where severalprocessing stations have a smaller length than the longest station, itis necessary to provide redundant space between the smaller processingstations in order for the indexing to function. The additional size ofthe apparatus due to the redundant space is a further source ofinefficiency in mandrel wheel printing systems.

There is a need for a printing apparatus that can overcome the problemswith mandrel wheel apparatuses while retaining the advantages of highvolume printing provided by staggered index processing.

SUMMARY OF INVENTION

In a first aspect of the present invention, a printing apparatus forprinting onto objects is provided, the apparatus comprising: a pluralityof carrying devices for carrying objects to be printed on, the carryingdevices each comprising a rotatable handling device configured to holdand rotate an object; a track defining a path along which each of theplurality of carrying devices can be moved; a plurality of processingstations comprising locations at which carrying devices are stationaryor moving while the carried objects undergo a process, arranged alongthe track and comprising at least one printing station; and a controllerconfigured to independently control the position and speed of each ofthe carrying devices with respect to each other along the track.

This invention therefore allows objects to be moved for example betweenprocessing stations while other objects remain stationary.

The provision of an apparatus in which a plurality of carrying devicescan be moved around a track independently of each other is advantageousover known printing systems as it enables printing systems in whichprocesses requiring object movement can occur simultaneously withprocesses requiring a stationary object, printing systems in which thedistance between neighbouring processing stations is not limited by thefootprint of the largest processing stations, and printing systems inwhich parallel printing operations allow a throughput to be achievedthat is not limited by the throughput of the slowest processing station,thereby enabling the most optimally compact machine design.

Preferably, the controller is configured to allow at least one of theplurality of carrying devices to be moved with a first speed, which maybe zero speed, on the track while at least one other of the plurality ofcarrying devices is moved with a second speed on the track, wherein thesecond speed is not equal to the first speed.

Preferably, the plurality of processing stations further comprises oneor more of: at least one drying station, at least one loading station,and at least one unloading station.

Preferably, the controller is configured to control the position andspeed of each carrying device such that each carrying device isstationary or moved at a first speed while an object is printed on atthe at least one printing station, and each carrying device is moved ata second speed through the at least one drying station, wherein thesecond speed is not equal to the first speed.

Preferably, the controller is configured to allow one of the pluralityof carrying devices to be stationary or move at a first speed at aprinting station while another of the plurality of carrying devices ismoved at a second speed through a drying station.

Preferably, the handling device is arranged to rotate an object at atleast one of the plurality of processing stations by coupling to adriving device at the at least one processing station such that torqueis transmitted from the driving device to the handling device.

Preferably, the printing apparatus comprises a rail or pad mountedadjacent to the track and wherein the handling device comprises a wheelconfigured to contact the rail or pad as it moves along the track,thereby causing the handling device to rotate as it is moved along thetrack.

Preferably, the track forms a closed path on which the carrying devicescan be moved.

Preferably, at least one of the processing stations is repeated on thetrack, thereby allowing multiple objects at different positions on thetrack to undergo the same process simultaneously.

Preferably, the controller is configured to move at least one carryingdevice such that it passes through, without processing, a first of arepeated processing station at which the carried object would normallybe processed, and instead be processed at a second of the repeatedprocessing station of the same type, thereby allowing the firstprocessing station to be inoperative without interrupting operation ofthe apparatus.

Preferably, the plurality of processing stations comprises at least twoprinting stations that are disposed parallel to each other butpositioned to be offset along their axis of printing.

In a second aspect of the present invention, a method of using theprinting apparatus of the first aspect is provided, the methodcomprising moving a first carrying device along the track at a firstprocessing station while a second carrying device remains stationary ata second processing station, wherein both carrying devices are disposedon the same track. In this way it is possible for the first processingstation to process multiple objects while the second processing stationis processing a single object.

In a third aspect of the present invention, a method of printing onobjects is provided, the method comprising: moving a first carryingdevice configured to carry a first object into the vicinity of a firstprocessing station configured to perform a first process; moving thefirst carrying device into an idle position, while moving a secondcarrying device configured to carry a second object into the vicinity ofthe first processing station; moving the first carrying device to asecond processing station configured to perform a second process, whileat the same time moving the second carrying device to a third processingstation configured to perform the second process.

The above steps provide a method of printing on objects that allowsparallel processes to take place in series with individual processes ona closed track, thus allowing for an increased throughput over knownmethods.

Preferably, the duration of the second process is greater than theduration of the first process.

Preferably, the method comprises moving a third carrying deviceconfigured to carry a third object from the vicinity of the firstprocessing station into the idle position, while the first and secondcarrying devices remain at the second and third processing stationsrespectively.

Preferably, the first process comprises at least one of: loading,inspecting, unloading, cleaning, surface energy modifying, printing,coating, drying, curing or fixing an object carried by a carryingdevice, and, preferably, wherein the second and third processingstations are printing stations and the second process comprises printinga single colour onto the surface of the object.

Preferably, the method comprises keeping the first and second carryingdevices at the second and third processing stations while first andsecond objects held by the respective carrying devices are printed on.

Preferably, the method comprises moving the first and second carryingdevices together into fourth and fifth processing stations eachconfigured to perform a printing operation with the same single colouras each other, wherein the colour is not the same as the colour printedin the second and third processing stations; and printing onto the firstand second objects held by the first and second carrying devices.

Preferably, the track is a closed track.

In a fourth aspect of the invention, there is provided method ofoperating a printing apparatus comprising: a plurality of carryingdevices for carrying objects to be printed on, the carrying devices eachcomprising a rotatable handling device configured to hold and rotate anobject; a track defining a path along which each of the plurality ofcarrying devices can be moved; a controller configured to independentlycontrol the position and speed of each of the carrying devices withrespect to the track; and a plurality of processing stations arrangedalong the track and comprising at least one printing station, wherein atleast one of the processing stations is repeated on the track, themethod comprising: moving at least one carrying device such that itpasses through, without processing, a first of a repeated processingstation at which the carried object would normally be processed, andinstead be processed at a second of the repeated processing station ofthe same type, thereby allowing the first processing station to beinoperative without interrupting operation of the apparatus.

By providing an apparatus having duplicated processing stations, andpassing through selected processing stations without stopping, it ispossible for the stations be deactivated during, for example,maintenance, servicing or replacement of a processing station, withoutinterrupting operation of the apparatus.

The apparatus and method of the present invention are applicable to awide range of printing processes, including but not limited toconventional contact means (e.g. offset lithography and flexography),digital contact means (e.g. electrophotographic printing, digital offsetprinting and belt transfer printing) and digital non-contact means (e.g.inkjet printing, electrostatic inkjet printing and piezoelectric inkjetprinting).

Printing typically takes place at one or more printing stations that arearranged along the track. The printing stations typically form a subsetof a greater number of processing stations arranged along the track,which may also include loading/unloading stations, drying stations,curing stations and other treatment stations.

In some embodiments of the invention different printing methods arecombined. For example, a first printing station may use offset printingto apply a first printed layer to the object, such as a white baselayer, while subsequent printing stations may use digital printing, suchas inkjet, to print a process colour image on the surface of the object.

The apparatus and method of the present invention are applicable toprint processes using one or more of a variety of inks, including butnot limited to water based inks, hydrocarbon solvent based inks and UVcurable inks. Colour printing may be performed according to a processcolour model (e.g. CMYK and extended gamut models: Hexachrome, CMYKOGV,and CMYKRGB). Spot colour inks may be used, including white, metallicinks, fluorescent inks, clear coatings and functional inks (e.g.magnetic).

The following disclosure also provides examples of specific indexingschemes using the apparatus of the present invention which provide anincreased throughput and/or a reduced total size in comparison withequivalent systems using mandrel wheels.

The present disclosure describes printing processes with reference toprinting on the body of necked or un-necked cylindrical monobloccontainers, but the apparatus and method of the present invention isapplicable to printing “direct to shape” on a wide range of objectsincluding such as cans, bottles, tubes, pots, cups or other containersor caps (e.g. wine bottle screw caps). Materials that the object is madeof may include metal, coated metal, pre-printed material, plastic,paper, card. The objects to be printed are preferably cylindrical butmay be of other geometries.

Aspects of the present invention will now be described by way of examplewith reference to the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic block diagram of printing apparatus according toone embodiment of the invention.

FIG. 2 is a schematic block diagram of printing apparatus according tosecond embodiment of the invention.

FIG. 3 is a schematic block diagram of printing apparatus according tothird embodiment of the invention.

FIGS. 4A-E illustrate an example of steps in a sequence performed duringoperation of the apparatus shown in FIG. 3.

FIG. 5 is a schematic block diagram of printing apparatus according to afourth embodiment of the invention.

FIGS. 6a and 6b are perspective views of a magnetic rotation couplingused to drive the rotation of object handling devices in someembodiments of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention provides a printing apparatus and method ofprinting in which carrying devices are provided along a track and areindependently moveable with respect to each other along the track. Theuse of independently moveable carrying devices provides the possibilityfor far more flexible indexing schemes than are possible in knowndevices.

The following disclosure provides examples of specific indexing schemesusing the apparatus of the present invention which provide an increasedthroughput and/or a reduced total size in comparison with equivalentsystems using mandrel wheels.

FIGS. 1 and 2 show examples of printing apparatuses 100 according toembodiments of the present invention. In each embodiment the apparatuscomprises a track 102 on which a plurality of carrying devices 104(hereafter “carriages”) are disposed and along which the carriages 104can move.

A plurality of processing stations 106 are arranged along the track 102,and each of the plurality of carriages 104 is configured to carry acontainer 108 successively into the vicinities of each of the processingstations 106. In the embodiment shown in FIG. 1, the processing stations106 comprise a loading station 106A, an inspection station 106B, fourprinting stations 106C which each print a different colour separation(cyan, magenta, yellow and black), a drying station 106D, a coatingstation 106E and an unloading station 106F. In the embodiment shown inFIG. 2, the processing stations 106 comprise a loading station 106A, aninspection station 106B, eight printing stations 106C which each print adifferent colour separation (white, cyan, magenta, yellow, orange,green, violet and black), a drying station 106D, a coating station 106Eand an unloading station 106F. Each processing station is configured toperform a process on one container 108 at a time, other than the dryingstation 106D which may process up to five containers 108 simultaneously.

The series of processing stations 106 of FIGS. 1 and 2 are chosen toprovide a printing apparatus in which objects 108 are loaded, inspected,printed upon using a four or eight separation printing process, dried,coated and unloaded. The skilled person will understand, however, thatthe number, type and order of processing stations described withreference to this figure and the following figures can be varied withinthe scope of the present invention for use in other applications.Examples of further types of processing stations that may be used withinthe scope of the present invention are cleaning (contact ornon-contact), pre-coating, pre-treatment for modifying surface energysuch as plasma or flame treatment, curing of a coating or print, andfixing of print.

In some embodiments, the apparatuses of FIGS. 1 and 2 comprise acleaning station (not shown) before the printing stations 106C forremoving dust or other dirt from objects before printing. The cleaningstation may be positioned before the inspection station 106B, after theinspection station 106B or may be combined with the inspection station106B. The cleaning station may comprise an air-knife cleaner forremoving dust particles from the surface of the object.

In some embodiments, the apparatuses of FIGS. 1 and 2 comprise a printquality inspection station (not shown) positioned after the printingstations 106C. The print quality inspection station comprises one ormore cameras arranged to inspect the quality of the print applied at theprinting stations 106C.

A control device 110 communicates with each of the carriages 104, eitherdirectly or via the track 102, in order to control the position andspeed of each of the carriages 104 independently with respect to thetrack 102.

Each carriage 104 is coupled to the track 102 firstly by means of aconstraining force and secondly by means of a motive force. Theconstraining force requires the carriage to move only along the path ofthe track 102 and allows the carriage 104 to be guided along the trackwith high precision. In some embodiments carriage 104 comprises linearbearings that engage with the track. The engagement between the linearbearings 104 and the track 102 constrains the motion of the carriage 104to one degree of freedom.

In this example, the motive force between the carriage 104 and the track102 is provided by a magnetic linear motor system. The carriages 104comprise permanent magnet elements that couple electromagnetically to asystem of electromagnets spaced around the track 102. A position sensingsystem measures the position of each carriage 104 on the track 102 and acontrol device 110 is used to control the position, speed andacceleration of each carriage 104 on the track 102 by controlling themagnetization of the electromagnets spaced along the track 102. Thecontrol device 110 will typically be programmed to move the carriages104 between processing stations 106 according to a predeterminedsequence, with the amount of time that each carriage 104 spends at eachstation 106 being determined in advance.

In some embodiments the motive coupling between the carriages 104 andthe track 102 may not be via a magnetic linear motor system and mayinstead be via another system that allows each carriage to moveindependently with respect to the track 104. In one alternativeembodiment, individually controllable rotational wheels are mounted oneach carriage 104 and are in contact with the track 102. In anotheralternative embodiment, the carriages 104 are mechanically coupled to atrack 102 using a clutch system that allows each carriage speed to bevariably controlled. In the above described alternative embodiments, thecontroller may communicate directly with the carriages 104 via awireless interface or may communicate via active or passive transpondersembedded in the track.

Examples of suitable track systems for use in the present invention arePrecision Track Systems from HepcoMotion and the iTRAK Intelligent TrackSystem produced by Rockwell Automation.

According to the embodiment of FIG. 1, the track 102 forms a closedpath, which allows carriages 104 to make repeated loops of the pathwithout a delay at the end of a cycle while the carriage 104 returns toits start position. In this embodiment the track 102 is substantiallydisco-rectangular in shape, having two horizontal linear sections, 102Aand 102B, that are vertically offset from each other. A first end of theupper linear section 102A is connected to a first end of the lowerlinear section 102B by a semi-circular arc 102C that lies in asubstantially vertical plane. Similarly, a second end of the uppersection 102A is connected to a second end of the lower section 102B byanother such arc 102D. Other shapes of closed track 102 are possible andmay be beneficial depending on the requirements of the processes beingused (e.g. as a result of preferred orientations of operations ofprocessing apparatuses). In some other embodiments, the track may havevertical linear sections along which processing stations are arranged,and which are connected to each other at their top and bottom bysemi-circular arc sections. In other embodiments, linear sections maynot be parallel nor lie in the same plane.

The carriages 104 comprise handling devices which in this embodiment arerotating mandrels adapted to carry containers. Each mandrel is mountedto its respective carriage 104 via bearings that allow the mandrel torotate around its central axis, and thereby rotate an attached containerabout its central axis, which is coaxial with the mandrel.

In some embodiments, the handling devices may be adapted to carryobjects using a holding device such as internal or external retainingclips or neck holding chucks. The holding devices may be adapted forholding other objects to be printed on.

Handling devices are capable of rotating about their axes when driven.The drive for rotating a handling device may be achieved in a variety ofways, including a servo motor mounted on the carriage, powered andcontrolled via connections to the carriage via a power track, data trackor wireless means. Alternatively the carriages 104 may be passive,whereby drive to the handling device is achieved by coupling rotationalmotion to the handling device from a drive device not located on thecarriage. Preferably the carriages 104 are passive requiring no externalservices in the form of electrical supply, control wiring, pneumatic orother connections to retain the object.

Coupling of rotational motion to the mandrels (or other handlingdevices) is provided at processing stations 106 where the processrequires the object to be rotated. The drive (the source of therotational motion) may be an individual servo motor, a geared or beltdrive from a common motor that serves a number of adjacent stations, astator coil that generates a rotating magnetic field, etc. The couplingmay be provided by a mechanical or by a magnetic force, or a combinationof these. This feature is discussed in more detail with reference toFIG. 6.

The drying station 106D may comprise an air pump or fan for forcing airover the surface of a printed object in order to evaporate liquid in thedeposited ink and extracting evaporated vapour.

In other embodiments a pinning or curing station may be provided insteadof or in addition to the drying station 106D. In some embodiments thepinning or curing station includes a means for providing one or more ofinfrared radiation, ultraviolet radiation and induction heating to thesurface of a printed object.

The drying station 106D may extend along a section of the track 102wherein objects are controlled to move continuously through the drier,rather than indexed between discrete positions. Drying 106D or pinningor curing stations may be placed between printing stations 106C if theprinting process requires that ink is dried, pinned or cured between theprinting of different colour separations.

The coating station 106E applies a layer of over print varnish (OPV)over the surface of the printed and dried object. The varnish may beapplied by means of a roller or a spray coater. The OPV itself impartsbeneficial properties to the printed object such as gloss, abrasionresistance, etc, and may be chosen for compatibility with the objectsurface material and inks. The varnish may be thermally curing, UVcuring, etc., and curing may be performed partially or completely aspart of the apparatus or by a separate curing oven downstream of theapparatus.

As a carriage 104 performs a single loop of the track 102, it visitsselected processing stations 106 sequentially. The steps set out belowdescribe an example of a series of processes that are undergone inrelation to one carriage during a single loop of the track 102 in theembodiments shown in FIGS. 1 and 2.

After unloading a printed container at the end of a previous cycle, thecarriage 104 is brought into the vicinity of a loading station 106A andstopped while an unprinted container 108 is brought to the loadingstation 106A by a conveyor (not shown). The container 108 is presentedin coaxial alignment with the mandrel of the carriage 104 andtransferred onto the mandrel of the carriage 104.

From the loading station 106A, the carriage 104 carries the container toan inspection station 106B comprising a defect inspection device. Thecarriage 104 stops again at the inspection station 106B where thecontainer 108 is then rotated through at least one complete revolutionof the mandrel. During this rotation, the defect inspection devicechecks for any deformities or contaminants on the surface of thecontainer 108 that could be detrimental to the printing process.Rotation of the container 108 is achieved by a magnetic coupling betweenthe rotating motion of a drive device located at the inspection station106B and the mandrel/handling device, which is engaged when the carriage104 is stopped at the inspection station 106B. The inspection device maybe an optical camera system, an electrically conducting bar with anelectrical current detection system, or any other suitable surfaceinspection device. If a defect is detected the container 108 is ejectedfrom the mandrel at the inspection station 106B. Before moving on, themandrel may be checked to ensure the object has been unloadedsuccessfully, whereafter the empty mandrel continues through theapparatus in the normal way except that the processing steps at eachprocess station are disabled for the empty mandrel.

After a successful inspection, the carriage 104 and the container 108are moved to a first printing station 106C. There the container 108 isrotated on the mandrel with a speed and number of revolutionsappropriate to the printing process employed while the printing processtakes place. As described above, the printing process is not constrainedto any one method, but may include any suitable printing process that isadapted for, or capable of, printing onto containers. These may be aconventional contact printing method such as offset lithography,flexography or rotary screen printing, or a digital method such aselectrophotography or non-contact ink jet printing. For the example ofan inkjet method of printing in which a printhead has ejectors spacedmore widely than the printed pixels on the container surface, thecontainer 108 is rotated over multiple complete revolutions while thecarriage is at the printing station. During each revolution of thecontainer 108, as the printhead is ejecting ink in accordance with theimage to be printed, the printhead is moved in a direction parallel tothe axis of the container for a distance of one pixel spacing. Thiscontinues over the multiple revolutions of the container 108, resultingin full image coverage on the container 108 surface from multipleinterleaved passes of the container surface beneath the printhead.During other processes, a different number of revolutions may berequired.

As with the inspection station 106B, rotation of the container 108 at aprinting station 106C is performed by coupling the rotating motion ortorque of a drive located at the printing station 106C to the handlingdevice when the carriage is at the printing station 106C.

Registration of the print with the container 108 surface position isperformed at a printing station 106C by controlling the synchronisationof the printhead or print device in accordance with position signalsobtained by a non-contact read-head 611 reading the angular position ofa rotary incremental encoder ring 612 mounted on the handling device.

The encoder ring 612 has encoded thereon information that can be used toinfer the angular position of the handling device and, hence, theangular position of a container 108 thereon. A stationary read-head 611is mounted separately at a fixed position with respect to the track 102at a printing station 106C, where the handling device is rotated bycoupling to a drive device. The read-head 611 is configured to read theangular position data encoded in the encoder ring 612, when the carriage104 is in a position on the track 102 whereby the encoder ring 602aligns with the read head 611, and provide information to the controldevice 110. Suitable encoder devices are the TONiC™ optical read-headand RESM rotary encoder ring manufactured by Renishaw plc.

The use of stationary read-heads automatically provides the processcontroller at a given processing station the real-time data it needsabout the position of the container 108 currently at that station 106without the need to switch data permanently associated with a particularcarriage 104 between processing stations 106 as it progresses throughthe apparatus. It further eliminates the need for power or dataconnections to the carriage 104 for the purposes of reading the angularposition of the container 108 at a processing station 106.

The arrangement of a stationary read-head at a print station 106C,reading from an encoder ring 612 on the carriage 104, automaticallycompensates for errors in linear position of the carriage 104 at a printstation 106C, if the encoder ring is the same diameter as the objectbeing printed. This is because a small translational error or movementalong the track that moves the axis of the object relative to theprinthead, which would otherwise lead to a print registration error,appears to the read-head in the same way as a rotation of the encoderring 602 by the same tangential distance. Therefore, no printregistration error results from a small translational error of thecarriage position at a printing station.

The carriage 104 and container 108 are then moved to subsequent printingstations 106C at which subsequent print operations are carried outsequentially on the container 108. The subsequent print operations mayuse the same or different print method to the initial print operation inorder to add further process colour separations or spot colours. Thesubsequent printing stations 106C may act to increase the width of theprint beyond the width of a single print station by having a secondprint station of the same colour ink as the first but displaced withrespect to the first in a direction along the axis of printing (the axisof printing being defined here as the direction of the line of an arrayof ejectors or nozzles of a printhead or contact line with the containerof a print roller, etc.) In general, the sequence of printing stations106C that operate on a container may comprise a variety of printingmethods to achieve a desired effect. Control of the rotation andregistration of the print to the container 108 surface are performed ateach printing station 106C in the same manner as in the first printingstation 106C.

In embodiments in which a print quality inspection station is providedafter the printing stations 106C, the object may be rotated at a lowerrotational velocity at the print quality inspection station than at theprinting stations 106C (for example, 3 rps compared with 5 rps) in orderto account for a camera data acquisition speed that is lower than theprint speed.

Once printed, the carriage 104 and container 108 pass through a dryingstation 106D. The dryer 106D may be implemented such that the carriages104 carrying the printed containers 108 move continuously through thedryer 106D rather than halting in one or more stations. Drying in thisexample is by airflow, but other examples may use heated air, infra-redradiation, induction heating of the container body, ultravioletradiation, etc. Because the carriages 104 of the present invention areindependently moveable, it is possible for one carriage 104 to passcontinuously through a drying station 106D while other carriages 104 arestopped at other processing stations 106.

In one embodiment, containers 108 are rotated as the carriages 104 movethrough the dryer by the rolling contact of a wheel mounted on eachhandling device with a rail mounted parallel with the track. The wheelis turned by its rolling contact with the rail as the carriage movesalong the track, thereby causing the container 108 to rotate. Such arail may be mounted at any position on the track at which it isdesirable to rotate the container 108 as the carriage moves along thetrack. A short rail or pad may also be usefully positioned prior to astation 106 at which a handling device is rotated by a driving device610, in order to provide some initial angular momentum in the directionof rotation to provide a faster synchronisation of the coupling at thestation 106.

Following the drying process, the carriage 104 and printed container 108are brought to a coating station 106E where an over-print varnish (OPV)is applied. The varnish is applied by a roller that transfers acontrolled layer of OPV from an anilox roller to the container 108surface. During this operation the container 108 is rotated at least onecomplete revolution via the magnetic coupling in the same manner as atthe inspection station. The OPV is typically a thermally curableformulation, which, when dried and cured, gives the print a high degreeof protection from handling and abrasion.

The carriage 104 and the container 108 are then moved to the unloadingstation 106, at which the printed container 108 is removed from themandrel. In some embodiments the printed container is transferred onto avacuum type belt (not shown) that conveys the printed and varnishedcontainers 108 to a curing oven, which is separate to the apparatus forcuring of the OPV. After the printed container 108 has been unloadedfrom the carriage 104, the mandrel may be checked to ensure that thecontainer has been properly unloaded, after which the empty carriage 104returns to the loading station 106 to begin a subsequent cycle.

While the carriage 104 and container 108 are undergoing the processesdescribed above, other carriages 104 and containers 108 undergo the sameseries of processes at staggered timing. Thus, while one or morecontainers 108 are positioned at printing stations 106C, othercontainers will be at the inspection 106B and loading 106A stages of thesequence. In general, each container 108 visits each processing station106 in sequence. Each processing station 106 is also visited by eachcontainer 108 in the order that the containers 108 are added to thesystem. In order to maximise efficiency of the processes, eachprocessing station 106 should be active for as great a proportion of thetime as possible.

The above described apparatus and method are advantageous over themandrel wheel device described in the background section. The abovedevice allows one container 108 to be moved continuously through adrying station while other containers are held at printing stations 106.This provides greater flexibility in terms of possible simultaneousprocesses than in previously known devices. The above apparatus andprocess also allow for a system in which the distance betweenneighbouring processing stations 106 is not limited by the footprint ofthe largest processing station 106. This is possible because thedistance between the individually controlled carriages 104 can be variedaround the track.

FIG. 3 shows another embodiment of the present invention in whichprocessing stations 106 that have a slower processing cycle (i.e. whichrequire a longer time over which to perform a process on a container)are repeated along a path, while processing stations 106 with a fasterprocessing cycle are not repeated. Rather than sequentially visitingeach of the processing stations 106 in an apparatus, a carriage 104stops at every non-repeated processing station 106, but passes throughsome repeated processing stations 106 without stopping. This provides asystem in which more than one container 108 may undergo the same processsimultaneously at repeated processing stations 106, which allows slowerprocesses to be performed in parallel on a track 102. By performingslower processes in parallel, while performing faster processesserially, the throughput of the print process is increased in comparisonto printing apparatuses in which each container 108 visits everyprocessing station 106.

The printing apparatus of FIG. 3 comprises a loading station 106A, aninspection station 106B, eight printing stations 106C, a drying station106D, a coating station 106E and an unloading station 106F providedalong a track 102. In this example, the printing process performed byeach printing station 6C has a greater duration than the loadingprocess, the inspection process, the coating process and the unloadingprocess. The drying process of a single container 108 may be slower thanthe printing process; but, because the drying station 106D is able toprocess up to five containers 108 simultaneously, it has a greaterthroughput than each of the printing stations 106C.

The eight printing stations 106C comprise four pairs 112 of identicalstations 106C provided along the track 102. The first pair 112Ccomprises a first cyan printing station 112Ci and a second cyan printingstation 112Cii. The second pair 112M comprises a first magenta printingstation 112Mi and a second magenta printing station 112Mii. The thirdpair 112Y comprises a first yellow printing station 112Yi and a secondyellow printing station 112Yii. The fourth pair 112K comprises a firstblack printing station 112Ki and a second black printing station 112Kii.(The order C-M-Y-K of the process colours may be chosen differently tosuit the printing process used).

As each carriage 104 passes through the apparatus, it sequentially stopsat the loading station 106A, the inspection station 106B, the coatingstation 106E and the unloading station 106E. Rather than stopping ateach printing station 106C, a given carriage 104 stops at only the firstor second printing station 106C of each pair 112 of printing stations.Consecutive carriages 104 stop at alternating printing stations 106C,such that if a leading carriage 104 stops at the first printing station106C of each pair 112, the following carriage 104 will stop at thesecond printing station 106C of each pair 112, and the next carriage 104will again stop at the first printing station 106C of each pair 112, andso on.

The above arrangement of printing stations 106C has a greater throughputthan an equivalent apparatus in which each container 108 passes throughevery printing station 106C of the apparatus. Such a system is madepossible by using a printing apparatus in which carriages 104 can beindividually controlled. The provision of individually controllablecarriages 104 allows a first set of containers 108 to be sequentiallycarried through a series of faster stations (or carried into an idlewaiting area), while other containers 108 are held stationary (withrespect to the track) in a slower processing station 106.

The skilled person will understand that the principles of the abovedescribed apparatus can be applied to systems having a different numbersof printheads, e.g. three sets of six printheads. The combinations ofprintheads 106 used in a given embodiment will depend on the relativeprocessing times of different processes in the apparatus, as well as thespecific goals of the user.

FIGS. 4A-E show the steps in which a plurality of carriages, A, B, C, D,E and F, carry a plurality of containers through the inspection station6B and printing stations of the printing apparatus of FIG. 3. Thepositions of carriages and containers shown in FIGS. 4A-E are shown inthe sequence that they occur in a method according to an embodiment ofthe invention.

In FIG. 4A, a first carriage, A, is stationary at the inspection station106B where a first container that it is holding is inspected. At thistime, a second carriage, B, is stationary at the loading station 106Awhere it is loaded with a second container.

In FIG. 4B, carriage A is moved into idle position 402 and stopped,while the second container held by carriage B is inspected at theinspection station 106B. At this time, a third container is loaded ontoa third carriage, C.

In FIG. 4C, after the inspection of the second container is complete,carriages A and B are moved together to the pair of cyan printingstations 112C, with carriage A at the second cyan printing station112Cii and carriage B at the first cyan printing station 112Ci. The cyanprinting stations 112C begin printing on the first and second containersheld by carriage A and carriage B respectively. At the same time,carriage C is moved to the inspection station 106B, where the thirdcontainer inspected, and a fourth container is loaded onto a fourthcarriage, D, positioned at the loading station 106A.

In FIG. 4D, carriage C is moved into the idle position 402, whilecarriage D is moved to the inspection station where the fourth containeris inspected. A fifth carriage E is moved to the loading station 106Awhere it is loaded with a fifth container. Because the printing processat the printing stations 112Ci and 112Cii has a longer duration than theloading and inspection processes, carriages A and B remain at, andcontinue printing, in the cyan printing stations 112Ci and 112Ciirespectively.

In Figure E, the cyan printing process has been completed and carriagesA and B are moved together to the pair of magenta printing stations112M. At approximately the same time, the inspection of the fourthcontainer is completed, and carriages C and D are moved together to thecyan printing stations, 112Ci and 112Ci, with carriage C moving from theidle position 402 to the second cyan printing station 112Cii andcarriage D moving from the inspection station 106B to the first cyanprinting station 112Ci without stopping in the idle position 402. At thesame time, carriage E is moved to the inspection station 106B and afifth carriage, F, is loaded with a fifth container at the loadingstation 106A.

For an apparatus in which processes are performed only in series, thetotal throughput of the apparatus is limited by the throughput of theslowest element.

For example, if the slowest process step is printing, having astationary printing duration of 0.8 seconds and a time to index betweenprinting stations of 0.2 seconds, the maximum throughput through theprinting station, and therefore the entire apparatus, is 1 container persecond (60 containers per minute).

By using parallel printing processes, the total throughput of theapparatus can be increased beyond the throughput of a slowest process inthe cycle. Table A below shows a detailed example of a process sequenceusing the printing apparatus of FIG. 3 to perform slow processes inparallel. It can be seen that while the printing stations 106 have astationary printing duration of 0.8 seconds and a time to index betweenprinting stations of 0.4 seconds, the apparatus is capable of providinga throughput of 2 containers per 1.2 seconds, equivalent to 100containers per minute.

Details of the process timings for each stage of the sequence are givenin Table A.

TABLE A Process step$\frac{{Distance}\mspace{14mu}\lbrack m\rbrack}{{Duration}\mspace{14mu}\lbrack s\rbrack}$Simultaneous process step$\frac{{Distance}\mspace{14mu}\lbrack m\rbrack}{{Duration}\mspace{14mu}\lbrack s\rbrack}$1 Empty carriage A arrives at Loading station. 2 Carriage A at Loadingstation while object A is loaded onto holder A.$\frac{0.0\mspace{14mu} m}{0.3\mspace{14mu} s}$ Object Asubsequently remains on holder A for entire machine sequence. 3 Movecarriage A to Inspection station.$\frac{0.1\mspace{14mu} m}{0.3\mspace{14mu} s}$ Empty carriage Barrives at Loading station. 4 Carriage A at Inspection station whileobject A is rotated and examined for$\frac{0.0\mspace{14mu} m}{0.3\mspace{14mu} s}$ Carriage B atLoading station while object B is loaded onto holder B.$\frac{0.0\mspace{14mu} m}{0.3\mspace{14mu} s}$ defects. If a defectis found Object B subsequently the object is ejected from remains onholder B for its holder and the carriage entire machine sequence.continues its sequence with an empty holder. 5 Move Carriage A to Idleposition. $\frac{0.1\mspace{14mu} m}{0.3\mspace{14mu} s}$ Movecarriage B to Inspection station.$\frac{0.1\mspace{14mu} m}{0.3\mspace{14mu} s}$ 6 Carriage A at Idleposition. $\frac{0.0\mspace{14mu} m}{0.3\mspace{14mu} s}$ Carriage Bat Inspection station while object B is rotated and examined for$\frac{0.0\mspace{14mu} m}{0.3\mspace{14mu} s}$ defects. If a defectis found the object is ejected from its holder and the carriagecontinues its sequence with an empty holder. 7 Move Carriage A throughPrint 1(i) station without stopping to Print 1(ii)$\frac{0.2\mspace{14mu} m}{0.4\mspace{14mu} s}$ Move Carriage Bwithout stopping through Idle position to Print 1(i)$\frac{0.2\mspace{14mu} m}{0.4\mspace{14mu} s}$ station. station. 8Carriage A at Print 1(ii) station while object A is rotated and printedonto. $\frac{0.0\mspace{14mu} m}{0.8\mspace{14mu} s}$ Carriage B atPrint 1(i) station while object B is rotated and printed onto.$\frac{0.0\mspace{14mu} m}{0.8\mspace{14mu} s}$ 9 Move Carriage Athrough Print 2(i) station without stopping to Print 2(ii)$\frac{0.2\mspace{14mu} m}{0.4\mspace{14mu} s}$ Move Carriage Bthrough Print 1(ii) station without stopping to Print 2(i)$\frac{0.2\mspace{14mu} m}{0.4\mspace{14mu} s}$ station. station. 10Carriage A at Print 2(ii) station while object A is rotated and printedonto. $\frac{0.0\mspace{14mu} m}{0.8\mspace{14mu} s}$ Carriage B atPrint 2(i) station while object B is rotated and printed onto.$\frac{0.0\mspace{14mu} m}{0.8\mspace{14mu} s}$ 11 Move Carriage Athrough Print 3(i) station without stopping to Print 3(ii)$\frac{0.2\mspace{14mu} m}{0.4\mspace{14mu} s}$ Move Carriage Bthrough Print 2(ii) station without stopping to Print 3(i)$\frac{0.2\mspace{14mu} m}{0.4\mspace{14mu} s}$ station. station. 12Carriage A at Print 3(ii) station while object A is rotated and printedonto. $\frac{0.0\mspace{14mu} m}{0.8\mspace{14mu} s}$ Carriage B atPrint 3(i) station while object B is rotated and printed onto.$\frac{0.0\mspace{14mu} m}{0.8\mspace{14mu} s}$ 13 Move Carriage Athrough Print 4(i) station without stopping to Print 4(ii)$\frac{0.2\mspace{14mu} m}{0.4\mspace{14mu} s}$ Move Carriage Bthrough Print 3(ii) station without stopping to Print 4(i)$\frac{0.2\mspace{14mu} m}{0.4\mspace{14mu} s}$ station. station. 14Carriage A at Print 4(ii) station while object A is rotated and printedonto. $\frac{0.0\mspace{14mu} m}{0.8\mspace{14mu} s}$ Carriage B atPrint 4(i) station while object B is rotated and printed onto.$\frac{0.0\mspace{14mu} m}{0.8\mspace{14mu} s}$ 15 Move Carriage Ato start of Drying station.$\frac{0.6\mspace{14mu} m}{1.2\mspace{14mu} s}$ Move Carriage Bthrough Print 4(ii) station without stopping to between Print$\frac{0.2\mspace{14mu} m}{0.4\mspace{14mu} s}$ 4(ii) station andstart of Drying station Move Carriage B to start of Drying station$\frac{0.5\mspace{14mu} m}{1.4\mspace{14mu} s}$ 16 Move carriage Athrough Drying station at constant speed while rotating$\frac{0.5\mspace{14mu} m}{2.5\mspace{14mu} s}$ Move carriage Bthrough Drying station at constant speed while rotating$\frac{0.5\mspace{14mu} m}{2.5\mspace{14mu} s}$ object A. object B.17 Move Carriage A to OPV station.$\frac{0.2\mspace{14mu} m}{0.2\mspace{14mu} s}$ Move Carriage B toOPV station. $\frac{0.2\mspace{14mu} m}{0.2\mspace{14mu} s}$ 18Carriage A at OPV station while object A is rotated and coated with OPV.$\frac{0.0\mspace{14mu} m}{0.4\mspace{14mu} s}$ Carriage B at OPVstation while object B is rotated and coated with OPV.$\frac{0.0\mspace{14mu} m}{0.4\mspace{14mu} s}$ 19 Move carriage Ato Unloading station $\frac{0.2\mspace{14mu} m}{0.2\mspace{14mu} s}$Move carriage B to Unloading station$\frac{0.2\mspace{14mu} m}{0.2\mspace{14mu} s}$ 20 Carriage A atUnload station while object A is unloaded from holder A.$\frac{0.0\mspace{14mu} m}{0.3\mspace{14mu} s}$ Carriage B at Unloadstation while object B is unloaded from holder B.$\frac{0.0\mspace{14mu} m}{0.3\mspace{14mu} s}$ Move carriage A toLoading station $\frac{0.5\mspace{14mu} m}{1.0\mspace{14mu} s}$ Movecarriage B to Loading station$\frac{0.5\mspace{14mu} m}{1.0\mspace{14mu} s}$

It should be understood that when reference is made to an object orcarriage being stationary, this refers to the position of the carriage104 along the track 102. The skilled person will understand that theterm “stationary” in this context includes the possibility of othermotions, including rotation of a handling device of the carriage and ofthe object about its axis.

The above example provides a detailed account of one scheme of parallelprocessing according to the present invention. It will be understood bythe skilled person that the above described concepts can be applied to awide range of printing apparatuses with differing functionalrequirements. The number of processes and parallel operations willdepend on the individual requirements of the apparatus.

For example, in another embodiment, pairs of objects to be printed couldbe loaded in parallel, inspected in series and then printed three at atime. In general, parallel processing can be made most efficient whenthe ratio of the durations of each operation most closely matches theratio of the number of parallel stations provided for each operation.

Furthermore, a system as described above, having independent control ofthe movement of objects and having replicated processing stations,provides redundancy that allows selected processing stations to bepassed through without processing, during, for example, maintenance,servicing or replacement of a processing station, without interruptingoperation of the apparatus.

FIG. 5 shows an apparatus in which the same set of eight printingstations 106C used in the apparatus of FIG. 3 may be configured in analternative way to increase the width of the print area rather than thethroughput of the machine. In this embodiment, for each pair ofprintheads 112, the first and second printheads are offset to each otherin a direction parallel to the axes of the objects to be printed by adistance of less than or equal to the print width from a singleprinthead 106C. An object is indexed through all eight printingstations, receiving a colour print process. The resulting print on theobject is up to twice the width of a single printhead 106C.

FIGS. 6A and 6B show an example of a magnetic rotation coupling system600 of a type that can be used at a processing station to drive theobject handling devices 104 of the above described embodiments. Thecoupling system comprises a driving device 610 (shown in FIG. 6A) havinga drive disc 601 that is rotated by a motor (not shown). The drivingdevice 610 is located at a processing station to drive a passivecoupling disc 603 that forms part of the movable carrying device 104.

In this example, the coupling comprises two non-magnetic discs, a drivedisc 601 at the processing station and a driven disc 603 on the carriage104. The two non-magnetic discs, 601 and 603, carry permanent magnets,604, inset into the facing surfaces of the discs, 601 and 603, incomplementary patterns. When the axes of the two discs, 601 and 603, arebrought into alignment by the carriage 104 arriving at the processingstation, the driven disc 603 angle self-aligns to the drive disc 601angle thereby synchronising its rotation to the rotation of the drivedisc 601.

An advantage of using a driving system that is separate from thecarriages is that the carriages do not require any electricalconnections. The handling devices are passive devices in whichcontrolled rotation of the container is achieved via a coupling from adrive device located at a processing station where rotation of theobject to be printed is required. The absence of electrical connectionsin the carriages substantially reduces the difficulty of designing asuitable apparatus in which the carriages can independently move arounda track.

1. A printing apparatus for printing onto objects, the apparatuscomprising: a plurality of carrying devices for carrying objects to beprinted on, the carrying devices each comprising a rotatable handlingdevice configured to hold and rotate an object; a track defining a pathalong which each of the plurality of carrying devices can be moved; aplurality of processing stations arranged along the track and comprisingat least one printing station; and a controller configured toindependently control the position and speed of each of the carryingdevices with respect to the track, wherein the handling device isarranged to rotate an object at at least one of the plurality ofprocessing stations by coupling to a driving device disposed at the atleast one processing station such that torque is transmitted from thedriving device to the handling device.
 2. The printing apparatus ofclaim 1, wherein the controller is configured to allow at least one ofthe plurality of carrying devices to be moved with a first speed, whichmay be zero speed, on the track while at least one other of theplurality of carrying devices is moved with a second speed on the track,wherein the second speed is not equal to the first speed.
 3. Theprinting apparatus of claim 1, wherein the plurality of processingstations further comprises one or more of: at least one drying station,at least one loading station, and at least one unloading station.
 4. Theprinting apparatus of claim 2, wherein the plurality of processingstations further comprises at least one drying station, and wherein thecontroller is configured to control the position and speed of eachcarrying device such that each carrying device is stationary or moved ata first speed while an object is printed on at the at least one printingstation, and each carrying device is moved at a second speed through theat least one drying station, wherein the second speed is not equal tothe first speed.
 5. The printing apparatus of claim 2 to wherein thecontroller is configured to allow one of the plurality of carryingdevices to be stationary or move at a first speed at a printing stationwhile another of the plurality of carrying devices is moved at a secondspeed through a drying station.
 6. The printing apparatus of claim 1,comprising a rail or pad mounted adjacent to the track and wherein thehandling device comprises a wheel configured to contact the rail or padas it moves along the track, thereby causing the handling device torotate as it is moved along the track.
 7. The printing apparatus ofclaim 1, wherein the track forms a closed path on which the carryingdevices can be moved.
 8. The printing apparatus of claim 1, wherein atleast one of the processing stations is repeated on the track, therebyallowing multiple objects at different positions on the track to undergothe same process simultaneously.
 9. The printing apparatus of claim 8,wherein the controller is configured to move at least one carryingdevice such that it passes through, without processing, a first of arepeated processing station at which the carried object would normallybe processed, and instead be processed at a second of the repeatedprocessing station of the same type, thereby allowing the firstprocessing station to be inoperative without interrupting operation ofthe apparatus.
 10. The printing apparatus of claim 1, wherein theplurality of processing stations comprises at least two printingstations that are disposed parallel to each other but positioned to beoffset along their axis of printing.
 11. The printing apparatus of claim1, wherein the controller is configured to move a first carrying devicealong the track at a first processing station while a second carryingdevice remains stationary at a second processing station, wherein bothcarrying devices are disposed on the same track.
 12. A method of movingobjects along a track during a printing process, the method comprising:moving, along a track, a first carrying device configured to carry afirst object into the vicinity of a first processing station configuredto perform a first process; moving, along the track, the first carryingdevice into an idle position, while moving a second carrying deviceconfigured to carry a second object into the vicinity of the firstprocessing station; moving, along the track, the first carrying deviceto a second processing station configured to perform a second process,while at the same time moving the second carrying device to a thirdprocessing station also configured to perform the second process. 13.The method of claim 12, wherein the duration of the second process isgreater than the duration of the first process.
 14. The method of claim12 further comprising moving a third carrying device configured to carrya third object from the vicinity of the first processing station intothe idle position, while the first and second carrying devices remain atthe second and third processing stations respectively.
 15. The method ofclaim 12, wherein the first process comprises at least one of: loading,inspecting, unloading, cleaning, surface energy modifying, printing,coating, drying, curing or fixing an object carried by a carryingdevice.
 16. The method of claim 15, further comprising keeping the firstand second carrying devices at the second and third processing stationswhile first and second objects held by the respective carrying devicesare printed on.
 17. The method of claim 16, further comprising: movingthe first and second carrying devices together into fourth and fifthprocessing stations each configured to perform a printing operation withthe same single colour as each other, wherein the colour is not the sameas the colour printed in the second and third processing stations; andprinting onto the first and second objects held by the first and secondcarrying devices.
 18. The method of claim 12, wherein the track is aclosed track.
 19. A method of operating an apparatus comprising: aplurality of carrying devices for carrying objects to be printed on, thecarrying devices each comprising a rotatable handling device configuredto hold and rotate an object; a track defining a path along which eachof the plurality of carrying devices can be moved; a controllerconfigured to independently control the position and speed of each ofthe carrying devices with respect to the track; and a plurality ofprocessing stations arranged along the track and comprising at least oneprinting station, wherein at least one of the processing stations isrepeated on the track, the method comprising: moving at least onecarrying device such that it passes through, without processing, a firstof a repeated processing station at which the carried object wouldnormally be processed, and instead be processed at a second of therepeated processing station of the same type, thereby allowing the firstprocessing station to be inoperative without interrupting operation ofthe apparatus.
 20. The method of claim 15, wherein the second and thirdprocessing stations are printing stations and the second processcomprises printing a single colour onto the surface of the object.